There are many known kinds of tobacco smoking articles with filters for removal of nicotine and tar from tobacco smoke by mechanical entrapment of such substances.
The most commercially available at the present time are filter units comprising fibers of thermoplastic organic substances. Such fibers are usually packed in a variety of ways and have a diameter less than 10 .mu.m. For example, there are filters comprising cellulose acetate and polyamide fibers (cf., DE 3,413,362, Int.Cl. A 24 D 3/04, 1984).
The main disadvantage of the prior art filters with thermoplastic organic fiber is inadequate removal of nicotine and tar from tobacco smoke. Thus, the standard filter made of organic fibers provides a nicotine content in the condensate of up to 1.46 mg/cig with a packing density of tobacco of 128 kg/m.sup.3, and a tar content of up to 19.9 mg/cig, while the international normal values of nicotine and tobacco contents in the condensate are 0.6-1.0 and 6-15 mg/cig, respectively.
Therefore, attempts have been made to improve the effectiveness of entrapping nicotine and tar using inorganic fibers. One of such attempts is a filter disclosed in U.S. Pat. No. 4,729,389, Int.Cl. A 24 D 3/08, 1988. This Patent discloses a tobacco smoking article with a filter comprising an inorganic kaolin fiber having a diameter of from 1 to 5 .mu.m. The fiber contains alumina and silica in an amount of from about 95 to about 99.5 percent by weight.
The all-kaolin filter is uncomfortable in that, in smoking the cigarettes provided with such a filter, a smoker will draw, together with smoke, kaolin particles present in the mass of kaolin fibers. As a consequence, U.S. Pat. No. 4,729,389 proposes, as a preferred embodiment, a filter unit which consists of two parts: a first part, facing a tobacco rod, containing a kaolin fiber, and a second part, facing a smoker, made of a standard organic fiber. This embodiment achieves an improved entrapment of the nicotine and tar through the first part of filter with a subsequent entrapment of the kaolin particles from smoke. This filter unit has a total (standard) length of 27 mm. The kaolin part length of 6 mm provides a nicotine and tar content in the condensate of 0.89 and 10.71 mg/cig, respectively.
However, production of such filter units is fraught with difficulties. As a practical matter, industrial manufacture of an endless filter rod requires assembly from alternating kaolin and organic parts. The kaolin inorganic fiber becomes badly plastified, so it is difficult to maintain precise parameters of the kaolin parts (length, density, diameter) in industrial production.